A digital calibration request (DCR) contains the requirements for the calibration process that a customer places on a calibration laboratory. In addition, administrative information is communicated in order to be able to assign the request unambiguously, e.g. to the customer as well as to the calibration laboratory.
The DCR may include several customer requirements, e.g.:
The DCR shall also transmit administrative data, e.g.:
The digital calibration answer (DCA) corresponds to a digital document that can contain a statement regarding the digital calibration request (dcr) as well as provide further administrative data, e.g. accounting information (booking codes and account specifications such as IBAN and BIC) for the customer.
The DCA contains administrative data, e.g.:
The illustration shows the individual stages through which a calibration product periodically passes. The totality of these stages is called the simple calibration cycle. It can basically be divided into two sections:
The simple calibration cycle begins with the start of the calibration procedure of a calibration item (1). Measurements follow to determine the measured value (2). Afterwards, the measurement data are analysed (create measurement uncertainty budget 3) and a calibration certificate is created (4). This is followed by the transfer (return of the calibration item to the industrial client and the calibration certificate) to the user in industry (5). There, the calibration item is registered in the quality management area (6) with all its properties (keywords are: Measuring device list, inventory number, place of inventory, further properties from the areas of accounting, controlling, sales, purchasing, production, warehousing) and is finally transferred to the production (7) and optimisation processes (8). Due to internal or external requirements, the calibration object is cyclically returned (5) to the calibration laboratory for recalibration (9), where calibration begins anew (1).
The transfer phase (5) limits the amount of information exchanged between the calibration laboratory and the client. Nowadays, however, this point is no longer about technical bandwidth issues, but about transfer and format standards, safety aspects and traceability issues in the appropriate national or international legal framework.
This figure shows the extended calibration cycle. This cycle differs from the simple calibration cycle in that a company operates its own calibration laboratory, which is able to provide its own working standards for internal use. To do this, the company needs a calibration item that is considered a valid traceable transfer standard. If this is given, one or more physically very similar copies with (possibly only temporarily) very similar physical properties are created from the calibration item, the so-called working standards (j). These working standards are treated in the company's own calibration laboratory () as equivalent to a calibration product which would be sent to the higher-level, accredited calibration laboratory with lower measurement uncertainty. Here, the individual calibration stages () to () are also run through analogously to (a) to (d). It should be noted that the measurement uncertainty U(UL) of the calibration by the in-house calibration laboratory is larger than the measurement uncertainty U(aCL) that an accredited calibration laboratory is able to state. The reason for this fact is that in the measurement uncertainty analysis further terms are now added which are greater than zero in magnitude. Because all measurement uncertainty terms are added quadratically, i.e. without sign, according to the specifications of the GUM, the measurement uncertainty to be stated increases. Detailed information can be found in the Guide to the Expression of Uncertainty in Measurement2 (GUM). As a result, the measurement uncertainty increases and the product quality decreases at the same time.
ISO/IEC 17025 requires that a calibration certificate must have a number of features and unique identifiers to minimise the possibility of misunderstanding or misuse.
In order to enable unambiguous identifiability, a unique identifier is stored on most calibration certificates - in addition to the features required by ISO/IEC 17025.
Analogous to how a website is uniquely identified worldwide by a host name, e.g. www.ptb.de, by specifying a subdomain (www), a domain (ptb) and a top-level domain (de), a unique identification of a digital calibration certificate can also be made.
A unique identification could then be, for example, D-K-99462-01-01.DAKKS_AB.DE. The breakdown is shown in the following figure.
1234 represents an example of an identifier for the calibration certificate that is uniquely assigned in the calibration laboratory. Each country would receive a top-level domain whose server is operated by the respective national quality infrastructure. For example, Germany would receive DE as a top-level domain. Each public institution of the national quality infrastructure and each accredited service provider can have a domain assigned to it. For example, DAkkS could receive DAKKS_AB as its domain name. Finally, any designation could then be made internally as a sub-domain, e.g. D-K-99462-01-01.
A consumer expects compliance with technical quality standards when buying a product. In addition, manufacturers (companies) also need the possibility to check goods and services for compliance with their product requirements.
For this purpose, a national system for quality assurance and consumer protection is needed, which is called National Quality Infrastructure (QI).
In Germany, the role of the National Metrology Institute is assumed by the Physikalisch-Technische Bundesanstalt (PTB).
The Deutsche Akkreditierungsstelle GmbH (DAkkS) is a private-sector organisation that performs the function of the national accreditation body of the Federal Republic of Germany.
There are several national standards organisations in Germany. The best-known national standards organisation is the Deutsches Insitut für Normung e. V. (German Institute for Standardisation). (DIN).
The verification of compliance with standards as well as the performance of calibrations is often not carried out by the national institutes, but by accredited service providers, which are subdivided as follows:
After providing a DCC from a calibration laboratory to a customer, it should be ensured that the DCC is
To ensure this, the use of digital signatures from a PKI is recommended.